M12A-5 TEE adapter nightmare

[Simon]

I decided to use NMEA 2000 on M12A-5 connectors/cables going forward. Seems to be the unspoken standard in many other fields too. so I order a TEE piece so that I can tap into the network with my USB CAN bus adapter. Well the two devices talk to each other but the USB adapter just would not work. So after probing around I discover that the TEE adapter I got rewires the pinout. Only 2 of the pins "pass through" and the others are joined together in the same connector.

So I start looking around and find that all M12A-5 TEE adapters do this. What is going on? Obviously there is some standard, not the one I thought though.

[eutectique]

Is your tee piece a power tap, by any chance? You would only have power lines in this case.

[Simon]

No, I think it comes under sensors or something like that that M12A connectors are commonly used for. Something like pins 1 and 3 pass through but 2 and 4 are joined together. Seems the best place for NMEA 2000 stuff is not RS but Amazon!